We don't need to allow users to install applications directly from the email
client. Instead, application installation is a two step process; the user
must first save the APK and then find it on the filesystem.
If the user does not want to allow installation of applications from unknown
sources, we don't provide the ability to save.
NOTE: After saving, we still try to open the APK which generates an error
toast. We will be removing the auto-open-after-save feature in a separate CL.
bug 3351137
Change-Id: I0eb1bc8224a154792fe852757e4b23a3059f4392
91a1cf1db0